Advances in plasma processing have facilitated growth in the semiconductor industry. The semiconductor industry is a highly competitive market. The ability for a chip manufacturing company to be able to process a substrate in different processing conditions may give the manufacturing company an edge over the competitor. Thus, manufacturing companies have dedicated time and resources to identify methods and/or arrangements for improving substrate processing.
A typical processing system that may be employed to perform substrate processing may be a capacitively-coupled plasma (CCP) processing system. The plasma processing system may be built to enable processing in a number of process parameters each of them having a wide range. However, in recent years, the types of devices that may be processed have become more sophisticated and may require more process control. For example, devices being processed are becoming smaller with finer features and may require more precise control of plasma parameters, such as plasma density and uniformity across the substrate, for better yield. Gas flow across the substrate is an example of a process parameter affecting etch profile and etch rate uniformity.
To facilitate discussion, FIG. 1 shows a simplified schematic of a prior art plasma processing chamber. Plasma processing system 100 may be a single, double, or triple or multiple frequency capacitively discharged system. For example, radio frequencies (RF) may include, but are not limited to, 2, 27 and 60 megahertz (MHz). It may also be an inductively coupled system (ICP) or a CCP-ICP hybrid.
In the example of FIG. 1, a lower electrode assembly may be configured with at least a focus ring 102 and a chuck 104 for holding a substrate (not shown to simplify illustration) in place during plasma processing. The chuck 104 may be an electrostatic chuck (ESC), for instance, and may be supplied with RF power by an RF power supply (not shown to simplify illustration). A ground extension ring 110, which may be made from aluminum, may be separated from focus ring 102 by an RF insulator ring 108. Ground extension ring 110 may be covered by a cover ring 112, which may be made from quartz, to protect aluminum ground extension ring 110 from plasma during plasma processing.
As shown in the example of FIG. 1, an upper electrode assembly may be configured with at least an upper electrode 114, which may be built like a shower head. The upper electrode 114 may be grounded (not shown to simplify illustration).
During plasma processing, gas flow may be supplied via a conduit (not shown) and may pass through a gas distribution manifold 116. The gas may be electrically excited into plasma in a chamber gap 118. Plasma may be confined by a set of confinement rings (120a, 120b, 120c, and 120d). Neutral gas species may pass through a set of confinement-ring gaps (122a, 122b, 122c, and 122d), configured between the set of confinement rings (120a-d), and may be exhausted from the chamber through a valve in the wall by a vacuum pump (not shown).
In the example of FIG. 1, the plasma processing pressure may be determined by the gas conductance, i.e., the set of confinement-ring gaps (122a-d) to provide the gas flow. The overall gas flow conductance of the flow path from the gas distribution manifold to the exhaust mats depend on several factors, including but not limited to, the number of confinement rings and the size of the gaps between the confinement rings. For example, in a confined plasma reactor with very small chamber gap 118, the number of confinement rings in a set of confinement rings may be limited by the spatial constraint of the very small chamber gap 118. Each confinement-ring gap in the set of confinement-ring gaps (122a-d) may be adjustable by a shaft 124. The gaps may be controlled by the advance of shaft 124. As shaft 124 moves lower, confinement ring 120d may sit on the outer shoulder of ground extension 112 and gaps 122 may be collapsed, in order 122c, 122b, and 122a. 
Consider the situation wherein, for example, a leading-edge process application requiring an ultra-short gas residence time where one or more steps of the process may require flow conductance levels that exceed the maximum capacity of the gap control. In such a process, the substrate (not shown) may need to be unloaded from the plasma processing chamber 100 and processed in another chamber that can provide the required flow conductance.
As may be appreciated from the foregoing, the shorter gas residence times may require an increase in gas conductance across the substrate through the processing chamber. However, the gas conductance may be limited by the hardware features, e.g., the number of confinement rings in a set of confinement rings and/or the size of the gaps between a set of confinement rings, for confining plasma in processing chamber with very small chamber gap. Given the need to stay competitive in the semiconductor industry, enhancement to the capability of capacitively coupled plasma processing systems are highly desirable.